Headed Anchors in Concrete

[craigmcg]

I have a few questions that I'm hoping some of you may have some insight into. FYI, I'm basing my questions off of ACI 318-05.

1) Imagine that a 12" long anchor is being cast 6" into a slab. A 6" secondary pour is then cast atop the original slab once cured, thus creating a horizontal cold joint halfway down the anchor. If the anchor is subjected to tensile loads, how will the shear transfer through the joint? Is the effective depth the full 12" or only 6"?

2) Obviously the ACI code is very vague when it comes to the potential strength increase by adding supplementary reinforcement. Has there been any recent studies or papers published that quantify the potential increase? I only have the "Reverse Cyclic Loading" paper from the early 80's.

Thanks in advance.

 

[Lion06]

I would treat this as being cast in a single pour. The rod will act as shear friction reinforcement holding the two planes together.

 

[LobstaEata]

Check out ACI 355, "State of the Art Report on Anchorage to Concrete." This should provide a good treatise on the subject you are interested in.

Regarding the cold joint, if the head of the anchor is below the cold joint, it would seem to me that there would be a compression load transfer between the two surfaces in order to continue development of the shear cone until the failure plane reaches a free edge or yields the anchor. I suppose this would depend upon on edge distance, so this should be accounted for.

Reinforcement contributes to pullout strength by intercepting the shear cone by transferring load to the bar through shear friction. Apply the provisions of ACI318 Chapter 11 for guidance for the shear friction design method.

 

[civilperson]

All concrete is assumed to crack, the cold joint is the same as a monolithic pour, (both crack at the joint location).